Tonight the discovery channel is kicking off shark week. They do it every summer and linsey davis is here with an exclusive "gma" preview. Here's a tidbit you can share with people at the cocktail party. Did you know that there are sharks that can live in both saltwater and fresh water and there are hundreds of them in the louisiana bayou. Well, they're called bull sharks, about ten long and extremely aggressive. But local fishermen say there's an even bigger and deadlier monitor lurking in the waters. They call them voodoo sharks. It's discovery channel's shark week meets swamp people. What is this? Jesse, jesse! Reporter: Legend holds that a man-eating monster stalks the murky waters of louisiana's bayou. To learn more a shrimp boat crew joined a team from louisiana state university to track a vicious species of freshwater shark. I've been shot, I've been stabbed, I've been run over, but I've never been scared like I am right now to get in this water. Reporter: That's blimp, a shrimper who's fished these wears all his life plugging into the depths of danger below. Within no time it is surrounded. I've got to be crazy. Something strange happens, all the sharks around the cage flee. An even larger predator emerges from the depths. I see one coming up. Biggest one yet. Using new cameras including the robotic shark cam -- enough. Let's go. Reporter: Discovery channel follows the legend not just under the water but through the tales of the storied bayou. That's what they've been calling it down here, the voodoo shark. Voodoo shark. Reporter: It's the guy's voice of what's lurking beneath that definitely hooks people. All week we'll bring you sneak peeks of what's coming up on discovery channel's shark week. Something about the bayou that makes excellent a-plus level tv. What's lurking beneath? You're so right. I'll watch and I think jake will be watching this. Not safe for anybody under 2. Maybe not safe for anyone under 40. You'll never swim again. Linsey, thanks. Coming up, the trying to

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